Googlebot will try a few times before the pages drop from the index.
As for how long it takes for a page to get back in once the site is
back up, that really depends on a number of factors, such as how often
the site is crawled in general.

Googlebot can't know if or when a page will return when it gets an
error response (whether that's a network down, 404, or other error)
and since our primary aim is to have quality search results for users,
we don't want to keep pages that return these types of errors in our
index. The best way of handling these situations, therefore, is to
remove the pages, but continue to try to access them, then return them
to the index once we get a valid server response.

On Feb 19, 5:22 am, Barry  Schwartz wrote: